Types of Building Automation Systems
At the crudest level of energy management and control is the manual operation of energy using devices—the toggling on and off of basic comfort and lighting systems based on need. The earliest forms of energy management involved simple time clock- and thermostat-based systems. Indeed, many of these systems are still being used. Typically, these systems are wired directly to the end-use equipment and mostly function autonomously from other system components. Progressing with technology and the increasing economic availability of microprocessor-based systems, energy management has quickly moved to its current state of computer based, digitally controlled systems.
Direct Digital Control
Direct digital control (DDC) systems function by measuring particular system variables (temperature, for instance), processing those variables (comparing a measured temperature to a desired setpoint), and then signaling a terminal device (air damper/mixing box) to respond. With the advent of DDC systems, terminal devices are now able to respond quicker and with more accuracy to a given input. This increased response is a function of the DDC system capability to control devices in a nonlinear fashion. Control that once relied on linear "hunting" to arrive at the desired setpoint now is accomplished through sophisticated algorithms making use of proportional and integral (PI) control strategies to arrive at the setpoint quicker and with more accuracy.